The present invention relates to a pressure vessel for storing a gas serving to inflate an airbag for the protection of occupants of a vehicle, and, more particularly, to a pressure vessel having an outflow valve connected to the pressure vessel housing at a predetermined breaking zone and containing a piston which extends to a pyrotechnic system arranged in the vessel interior and which, when the pyrotechnic system is ignited, pierces the predetermined breaking zone of the housing and opens an outflow orifice for the gas.
A pressure vessel is shown German Auslegeschrift No. 2,118,745 where an outflow valve is arranged in the interior. The pressure vessel and is equipped with a piston which projects into a gas generator integrated in the vessel interior and the other end of the piston is connected to the wall of the pressure vessel in the region of a predetermined breaking zone. The piston has a cylindrical shape. After the ignition of the gas generator, the piston presses the predetermined breaking zone of the wall of the pressure vessel outwardly and thus opens an outflow orifice for the gas stored in the pressure vessel. The predetermined breaking zone is circular, so that, when the cylindrical piston is extended, an annular outflow orifice for the gas is obtained. The cross-section of this outflow orifice does not change in the course of the axial movement of the piston as far as its end position.
An object of the present invention is to provide a pressure vessel in which the outflow characteristic of the outflow orifice can be influenced in a controlled manner even during the opening movement of the outflow valve.
This object has been achieved in accordance with the present invention by providing an outflow valve which contains a control body adjoining the predetermined breaking zone and extending in the direction of the pyrotechnic system, the cross-section of which body changes in the axial direction of the outflow valve.
The size of the outflow orifice, the outer edge of which is determined by the contour of the predetermined breaking zone, is thereby varied during the opening movement of the outflow valve. As a result, the outflow of gas from the pressure vessel into the airbag can be influenced in time even during the opening movement of the outflow valve. The shape of the control body makes it possible, for example, to prevent an overload of the airbag at the start of the outflow operation by a smooth onset of the outflow characteristic.
In one currently contemplated embodiment of the present invention, the control body tapers in the direction of the pyrotechnic system. With an increasing opening movement of the outflow valve, therefore, the outflow orifice of the pressure vessel becomes larger.
In yet a further embodiment of the present invention, the predetermined breaking zone has a circular predetermined breaking line, and the control body is made rotationally symmetrical. This provides an annular outflow orifice which guarantees uniform outflow conditions.
In a further embodiment of the invention, the control body is provided with an outer contour curved in longitudinal section. It is thereby possible to obtain even a complicated outflow characteristic, such as, for example, an S-shaped characteristic of the pressure trend over the outflow time.
In a still further embodiment, the outflow valve is followed outside the pressure vessel by a diffuser with an inner wall widening in the axial direction towards the outflow valve and which centers and fixes the control body in its position opening the outflow orifice of the pressure vessel. The outflow valve thereby acquires a specific end position which at the same time defines the maximum outflow cross-section of the outflow orifice.